Department of Biological Sciences, University of Pittsburgh, Pittsburgh, PA 15260, USA.
Department of Ecology Evolution and Behavior, Princeton University, Princeton, NJ 08544, USA.
Curr Biol. 2019 Jul 8;29(13):2157-2166.e6. doi: 10.1016/j.cub.2019.05.074. Epub 2019 Jun 27.
Hox genes pattern the anterior-posterior axis of animals and are posited to drive animal body plan evolution, yet their precise role in evolution has been difficult to determine. Here, we identified evolutionary modifications in the Hox gene Abd-B that dramatically altered its expression along the body plan of Drosophila santomea. Abd-B is required for pigmentation in Drosophila yakuba, the sister species of D. santomea, and changes to Abd-B expression would be predicted to make large contributions to the loss of body pigmentation in D. santomea. However, manipulating Abd-B expression in current-day D. santomea does not affect pigmentation. We attribute this epistatic interaction to four other genes within the D. santomea pigmentation network, three of which have evolved expression patterns that do not respond to Abd-B. Our results demonstrate how body plans may evolve through small evolutionary steps distributed throughout Hox-regulated networks. Polygenicity and epistasis may hinder efforts to identify genes and mechanisms underlying macroevolutionary traits.
Hox 基因塑造了动物的前后轴，并被认为推动了动物体模式的进化，但它们在进化中的精确作用一直难以确定。在这里，我们确定了 Hox 基因 Abd-B 的进化修饰，这些修饰极大地改变了其在 Drosophila santomea 体模式中的表达。Abd-B 在果蝇 yakuba 中是必需的，果蝇 yakuba 是 D. santomea 的姐妹种，Abd-B 表达的改变预计会对 D. santomea 中体色素的丧失做出巨大贡献。然而，在当今的 D. santomea 中操纵 Abd-B 的表达并不影响色素沉着。我们将这种上位相互作用归因于 D. santomea 色素沉着网络中的另外四个基因，其中三个的表达模式已经进化，不再对 Abd-B 做出反应。我们的研究结果表明，体模式可能是通过分布在 Hox 调节网络中的小进化步骤来进化的。多基因性和上位性可能会阻碍识别基因和机制的努力，这些基因和机制是宏观进化特征的基础。
